Automatic Test Pattern Generation (ATPG) is used to find a test pattern (an input or test sequence) that, when applied to an IC, allows a tester to determine between correct circuit behavior and faulty circuit behavior caused by defects. The generated test patterns can be used to test ICs after manufacture (i.e., manufacturing testing). Manufacturing testing, however, may not be able to detect all defects associated with manufacturing. For example, infant mortality related defects may be difficult to detect.
Infant mortality relates to ICs that fail at a relatively higher rate over a short period of time due to manufacturing defects. Infant mortality failures are typically defined as those failures that cannot be detected during the manufacturing test of the IC and manifest themselves after a certain period in time when the IC is in an intended application. Inherent manufacturing defects, possibly those caused by contamination or process variability, that can cause IC's to have shorter lifetimes are referred to as infant mortality related defects. Infant mortality related defects may be weak resistive opens or shorts resulting in small additional delays.
Detecting infant mortality defects often depends on the defect size, defect location, clock speed and defective behavior. Presently, burn-in testing or current based testing techniques may be used to detect infant mortality related defects. Burn-in, however, can be expensive and destructive. Additionally, due to, for example, increased complexity and smaller feature sizes, current based tests such as IDDQ may not be as effective. This is especially true for smaller process nodes, such as 90 nm or smaller. At the smaller technology nodes, IDDQ and other current based tests can be rendered ineffective for detecting infant mortality related defects due to the background current leakage being high and a small difference between faulty and fault-free devices.